Dangerous high-power laser radiation has been used in technology for many decades, capable of damaging CCD and CMOS matrices (used in video cameras and lidars), as well as causing irreparable damage to the organs of vision. Damage occurs at a high-energy fluence density above a certain threshold value. The main disadvantages of the passive protection devices used – light filters – are color distortion and a narrow wavelength range that requires an accurate value of the wavelength of laser radiation that falls on a photosensitive material or device. The operation of a nonlinear optical limiter of laser radiation power for passive protection is based on the use of a material with a strong nonlinear optical response. However, existing materials do not have the low energy dimming threshold required for practice and, moreover, have insufficiently effective optical attenuation. Further improvement of these characteristics is necessary, although the results already achieved at the moment may well be used in practice. A nonlinear absorption coefficient was used to evaluate the effect of optical limiting. As a result of the studies carried out in this work on the example of composites of single walled carbon nanotubes with a tetra(cyclotriphosphazene)-substituted phthalocyanine ligand, we found that depending on the hydrodynamic radius of fine particles, the efficiency of optical limiting can increase by an order of magnitude. At the same time, the efficiency of optical limiting of composites is more than 2 times higher compared to the original nanotubes.
To protect photosensitive detectors and micro-optoelectromechanical systems, protective equipment is needed against the ingress of powerful laser radiation. Conventional color filters pose a problem for such devices by cutting out the region of the spectrum in which the laser operates. To ensure the possible operation, passive limiters based on nonlinear optical effects can be used. They are capable of transmitting non-hazardous laser radiation with insignificant attenuation (transmission of the order of 70%), and when hit by powerful laser radiation they can quickly darken. The urgency of this problem only increases with the development and widespread use of laser systems. In particular, when using lidars, receiving photosensitive detectors are often damaged. The use of various conjugates with carbon nanotubes is promising for creating limiters. In this work, it is proposed to use conjugates of dimeric phthalocyanine complexes of Cu to create nonlinear optical materials. This material demonstrates the ability to attenuate laser radiation with a nanosecond duration of 16 ns, even in the case of single pulses, due to the synergistic effect of absorption and scattering of radiation. In addition, in the case of 140 fs femtosecond periodic radiation, with a pulse repetition rate of 80 MHz, this material demonstrates the attenuation of radiation when using a cut-off diaphragm due to the effect of self-phase modulation (SSPM). The characteristics of the SSPM pattern were studied, it was noted that the outer rings have the greatest width. In general, the width of the rings gradually increases with distance from the center of the beam. At the same time, the peak fluence (highest fluence value) of each ring is approximately the same, with the exception of the central part. In the central region, a strong effect is observed from heated flows tending upward and thus strongly violating symmetry.
The effect of ultrashort laser radiation parameters on the process of biomaterial formation based on dispersed media of bovine serum albumin and carbon nanotubes was studied. It is noted that, in contrast to the use of continuous laser radiation of comparable power, the composite nanomaterial is formed when lower temperatures are reached, which provides additional advantages and a smaller change in the protein structure. This effect can also be associated with a pulse repetition rate of 80 MHz, in the interval, which is about 12.5 ns, partial cooling of the material can occur, while this effect is sufficient for the formation of a biomaterial. The hardness of this material is comparable to that of native tissue. A strong twofold change in the elasticity of such a material in comparison with drying in air indicates the formation of an inner framework of carbon nanotubes. The possibility of this effect is also confirmed by spectral studies, according to which, at the used wavelength of 810 nm, the radiation is absorbed mainly by carbon nanotubes and only as a result of heat transfer is transmitted to bovine serum albumin and is spent on water evaporation. In vitro studies of cell growth in the presence of biomaterial were carried out by quantitative (MTT test) and qualitative (microscopy) methods. It was found that the number of cells grown on the composites exceeds the number of cells in the control after 72 hours of incubation. The cells on the composites formed a monolayer, their morphology does not differ from the morphology of the cells in the control. In vitro studies indicate a positive effect of the biomaterial on cell adhesion and proliferation and, consequently, on the possibility of their use for tissue regeneration.
In this study, J-type dimeric copper phthalocyanine in dimethylformamide (DMF) was investigated to show strong nonlinear absorption due to the reverse saturable absorption (RSA) under single nanosecond pulses (16 ns at a wavelength of 532 nm), which significantly exceeds the lifetimes of excited states. In the case of a femtosecond laser, the effect of spatial self-phase modulation was observed, with no contribution from nonlinear absorption being found. The only linear absorption was detected under pulses of 140 fs at a wavelength of 790 nm. The femtosecond pulse repetition rate was 80 MHz which corresponds to a delay between single pulses of about 12.5 ns. Both analytical wavelengths used were outside the intense absorption region (Q- and B- bands) of J-type dimeric copper phthalocyanine in the UV/Vis/NIR spectrum. In the case of femtosecond laser radiation, a sufficient population of excited states was not achieved due to the low peak fluence (~ 0.03 mJ/cm2). For the single nanosecond pulses, the threshold fluence density was ca. 30 mJ/cm2. In the switch circuit, such material should be placed horizontally to exclude asymmetric thermal convection resulting from the gravity effect.
We studied the formation of a composite from an aqueous dispersed medium with albumin and carbon nanotubes under the action of laser radiation in continuous wave (CW) mode and pulsed mode with a repetition rate of 10 Hz and pulse duration of 16 ns. During the experiments, the temperature was monitored at the site of exposure, as well as its distribution in the liquid. Pulsed solid-state Nd:YAG laser and CW diode laser with an irradiation power of ∼500 mW were used as radiation sources. However, a three-dimensional composite was formed only with constant exposure. The effect of pulsed laser radiation with an intensity corresponding to nonlinear interaction with water dispersion led only to its enlightenment. Thus, it is important not only the energy parameters of radiation but also the frequency of energy portions exposure for the fabrication of tissue-engineered structures (composites). As a result, it was found that the curing of the dispersion and the composite formation occurs under the action of continuous or pulsed (with a high pulse repetition rate) laser radiation at a temperature in the range from 45°C to 50°C; in case the pulse repetition rate is insufficient, composite formation is not observed even under the action of high intensity radiation and heating occurs only to a temperature of ∼40 ° C. This formation process can be generated both in the visible 532 nm and in the infrared 810-nm wavelength ranges. In this case, one of the main conditions is the absence of albumin or cells absorption at these wavelengths so that absorption occurs mainly with single-walled carbon nanotubes. Studies of the surface and internal structure of the composite made it possible to demonstrate the binding of nanotubes to each other. This happened under the influence of laser radiation. This led to high hardness values of the composites. The average value of hardness was 0.26 ± 0.02 GPa.
At present, laser sources are widely used in many fields. Not only in laboratories, but also in sphere of medicine, manufacturing and military. Lasers are potentially dangerous to the eyes or sensitive optical devices, therefore it is necessary to develop optical limiters. One of the significant properties of carbon nanotubes is their optical limitation of laser radiation. Many works of scientific groups are devoted to materials for limiters, which include carbon nanotubes. However, they still have an increased interest. A particular role is given to such mechanism of nonlinear attenuation as scattering and absorption. Moreover, it is important not only their combined effect to increase the effectiveness of the limiters as a whole, but also the contribution of each of them with their combined effect. It is equally important to accurately determinate the concentration in which there is a strong attenuation of high-intensity laser radiation and minimal attenuation at low intensity. The nonlinear and linear optical properties of water-dispersed media with different concentrations of single-walled carbon nanotubes (SWCNTs) were obtained by optical density spectra, experimental Zscan data with an open aperture and a fixed location of the limiter. Radiation in single mode with duration of 16 ns at wavelength of 1064 nm from Nd:YAG laser was used. The linear transmittance of the prepared water dispersions of the SWCNTs ranged from 60% to 70%. Limiter with such working substances had attenuation coefficient 10 and 14 for the concentration of nanotubes 3.125 mg/l and 6.25 mg/l, respectively.
Laser radiation limiters can be made on the basis of working substances, which have strong nonlinear effects after reaching a certain critical value (threshold limiting). Thus, it becomes possible to obtain a high transmission for a safe beam and a sharply reduced transmission for a hazardous beam. To determine the nonlinear and linear optical properties of these materials there were carried out comprehensive spectroscopic studies, experiments by Z-scan methods with an open aperture and a fixed location of the limiter. Working substances was developed which is suspension of conjugates J-type phthalocyanine dimers Zn or Mg with single-walled carbon nanotubes (SWCNTs) in water. Created conjugates can be used not only for protecting eyes and light-sensitivity elements, but for forming three-dimensional tissueengineered structures. Using conjugates J-type phthalocyanine dimers Zn and Mg with SWCNTs will increase the optical absorption in the wavelength range of laser processing by reducing the thermal effect on other substances in the composition of this structure. The Nd:YAG laser was used as the laser radiation source for generating pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape of Gaussian type. The threshold of limiting, linear and nonlinear absorption coefficients were determined by output characteristic, that was obtained by fixed location of the limiter. Created working substances have values of the following order: linear absorption coefficient ~ 3 cm-1 for layer of 0.2 cm thickness, low limiting threshold ~ 1 MW·cm-2 and high value of the nonlinear absorption coefficient ~ 550 cm GW-1 . Knowing the nonlinear optical parameters, Z-scan data with an open aperture can be calculated for comparison with experimental data.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.